Why the difference in resale value?

I bought an Adcom 555 brand new from Tweeter HiFi in the mid 80’s.  I couldn’t wait until I could afford something better and never liked the sound.  I do not see why the love for Onkyo. At one time I sold the line and it was real junk, broke down often and sounded like nothing special.  While the Onkyo may have looked good on the outside, the inside was full of cheap parts, internal heat sinks could cut your hands to ribbons.  

P.S. I said I "enjoyed the heck out of" my original Adcom GFA 555. Thinking back -- it was a long time ago -- that really isn’t true. I remember that the treble always bothered me, Nelson Pass influence notwithstanding. I sent it out for modification and finally sold it. After an intermediate amp that sounded better but had transformer hum, I wound up with a Bryston 14B SST, which was another, far better, world of high fidelity. Better across the band!
I've never tried an Onkyo.

@mike_in_nc I have the 535L. I cannot be sure if it's Pass designed or not. I love the bass and the slam but the treble is a bit rough. Same experience. Bought in early 90s.

Probably just supply. Why would anyone actually care?

Hey out there.  I do appreciate all the perspectives coming from everyone.  It was fun - for a relative 'snoozer'!  Maybe I can spice things up a little.  So, "Fuzztone," you wonder why should I care in the first place.  Well, maybe because I would be looking to differentiate among historically well regarded yet affordable products of the same class currently on offer in the resale marketplace.  Or maybe I wouldn't, but I simply would want to see what you and others would have to say on an audio related topic of my choosing.  Or how about this even...it was a round about way of calling out those who must seize an opportunity to gain at the expense of the guileless, whether it be with audio sales or with auto sales.  Ebay audio sellers take heed...Sorry, but no way am I giving you double the original retail price for a 30+ year-old metered power amp, while I couldn't in my right mind ask for more than maybe 70% of original retail, at best, for a similarly priced and respected functional "black box" equivalent from back in the day.  Sell 'em if you got 'em - just not to me!